by In the field of microscopy, researchers from Japan have made significant strides in developing a new technique that allows for detailed examination of a material’s surface using evanescent waves. Unlike conventional microscopes that utilize active measurements, which involve irradiating a sample with light or electrons, this new method passively detects evanescent waves to obtain nanoscale precision in probing an object’s surface.
Evanescent waves are transient electromagnetic waves that do not carry energy, akin to ripples on a surface. They can be generated through the interaction of light with a material’s surface or through thermal means. As all matter contains energy and emits heat, localized heat fluctuations within a material can briefly produce strong evanescent waves. The researchers from the Institute of Industrial Science at The University of Tokyo have harnessed the power of passive detection to develop this groundbreaking form of microscopy.
Scanning near-field optical microscopy is a widely used technique to investigate material properties at the nanoscale level by analyzing scattered electromagnetic radiation. However, the research team, led by Ryoko Sakuma, has taken this a step further by utilizing thermal infrared wavelengths to observe previously undetectable details. The key advantage of this technique is that it relies on the object’s emitted radiation, eliminating the need for external illumination.
To demonstrate the efficacy of their approach, the researchers used their prototype instrument to examine thermally excited evanescent waves generated in two dielectric materials: aluminum nitride and gallium nitride. Notably, they observed unexpected weak scattering in the Reststrahlen band, an absorption band. This marked the first time such a phenomenon had been witnessed without any light exposure. Furthermore, their spectroscopic analysis revealed that only polariton waves, waves caused by surface phonon resonance, existed in the Reststrahlen band, contrary to theoretical predictions indicating the presence of significant thermal fluctuation. These findings deepen our understanding of thermally excited evanescent waves within this band and lay the groundwork for an enhanced passive detection model for identifying dielectric materials.
The research team is enthusiastic about advancing this technology further. According to senior author Yusuke Kajihara, their instrument is the world’s only capable of using terahertz wavelengths to observe nanoscale temperature distributions on surfaces. The terahertz wavelength range extends from the mid-infrared, starting at approximately 10 µm, up to 1 mm. Currently, their primary goal is to improve the functionality of the instrument, given that it is still a prototype. Kajihara emphasizes that this microscope technology is entirely novel and that they are still discovering its potential applications.
Moving forward, the team plans to enhance their prototype instrument and refine the technique. Their next step involves developing an improved detection model. Their ultimate aim is to achieve greater versatility, resulting in a non-destructive characterization technique that enables highly localized analysis of surface dynamics. This innovative form of microscopy holds immense promise in revolutionizing material examination and understanding in various scientific fields.
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1. Source: Coherent Market Insights, Public sources, Desk research
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